International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

The Upper Cretaceous intrusive rocks with extensive crustal contribution in Hacımahmutuşağı Area (Aksaray/Turkey)

Pages: 261 - 276

Authors: SERHAT KÖKSAL

Abstract: The Hacımahmutuşağı area (Aksaray/Turkey) is located in the western part of the Central Anatolian Crystalline Complex (CACC). Gneiss and marble compose the basement units, while intrusive rocks are gabbros and granitoids. The pegmatitic hornblende gabbros contain pegmatitic to fine-grained hornblendes, plagioclase, clinopyroxene, and accessory opaque minerals. The fine-grained gabbros, on the other hand, are composed of plagioclase, hornblende, and biotite as major components whereas the apatite and opaque minerals are present in accessory content. Granitic–granodioritic rocks are the common intrusive rock types in the area, and constitute quartz, orthoclase, plagioclase and biotite, and accessory zircon and opaque minerals. Leucogranites, comprising quartz, orthoclase, plagioclase with minor biotite, hornblende, and with accessory apatite and opaque minerals, are found as dykes intruding the marble and the granitic–granodioritic rocks. Strontium–neodymium isotope data of gabbros and granitoids have high 87Sr/86Sr(i) ratios (0.7076 to 0.7117) and low ɛNd(i) values (−5.0 to −9.8) point out enriched source and pronounced crustal contribution in their genesis. In the Hacımahmutuşağı area, it is plausible that the heat increase caused by the hot zone, which was generated by underplating mafic magma along with the hydrous mafic sills in the lower crust, might have resulted in partial melts from crystallized mafic sills and older crustal rocks. It can be suggested that these hybrid melts adiabatically rose to the shallow crust, ponded and crystallized there and formed the magma source of the intrusive rocks within the Hacımahmutuşağı area and the other hybrid granitic rocks with crustal signatures in the CACC. Geochemical data indicate that granitoids and gabbros are collision to post-collision related sub-alkaline rocks derived from an enriched source with extensive crustal inputs.

Keywords: Hacımahmutuşağı, Central Anatolia, granitoids, gabbros, Sr–Nd isotopes

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